give it another shot, tel her that u really care about her and that u want ur relationship 2 be more than just friendship. if u still get rejected than just accept it (or let her think that u have) theres nothing more of a turn-off than a guy who seems overly eager or turns into a stalker. trust me its happened to me b4, it'll just ruin all the chances that u have for being with her. she says "no" just say "ok" then just walk off and act all cool and try and hide ur tearing heart from her. she'll be like "what the, is that all he says?" then it gives off the impression that your not desperate and that SHES missing out on not being with YOU..then she'll feel like an idiot and give u more attention/
thats when u have her in the position u really want her...so when u see her next time, act like nothings happened like u never asked her out in the first place. it'll make her curious and u'll just ooze out confidence (which is oh-so-sexy). she'll want u more than ever before, but whatever u do, dont completely ignore her and act all fridgety because then she'll just think ur a big sook and that u cant handle rejection.
tip cut short: ask her out, she says no (u neva know mayb shes just waitin 4 u 2 ask her out again), act like nothings happened to u shes just like every other girl (lets just pretend that she is), she'll throw herself at you. and bingo u got ur girl!
if u go thru all that bloody trouble and she still dont want u, then get over her coz u deserve sum1 who is willing 2 put as much effort into the relationship as you do. plus u cant change her feelings..learn to deal with it, and maybe in the future it may work out 4 u both!
good luk with it!!